This will create a named pipe: /tmp/itm.fifo. Another application, e.g.
OpenOCD, will have to be connected (open+write) to this pipe. Here's an
example command for OpenOCD+GDB that does that. (But
read their documentation!).

(gdb) monitor tpiu config internal /tmp/itm.fifo uart off 8000000

itmdump will read from the pipe, parse the packets and write the payload
to stdout: